1. Field of the Invention
The present invention relates to an isobutylene polymer having an unsaturated group and a process for preparing the same.
2. Description of the Related Art
An isobutylene polymer having more than one unsaturated group per molecule on the average is cross linked and cured to produce a rubbery cured material. Such polymer can be modified by introducing a cross-linkable silicon group to form a moisture-curable polymer as disclosed in U.S. Pat. No. 4,904,732 and Japanese Patent Kokai Publication No. 6041/1988.
The isobutylene polymer having more than one unsaturated group per molecule on the average is disclosed in U.S. Pat. Nos. 3,644,315 and 4,524,187 and it is prepared by copolymerizing isobutylene and a compound having a conjugated double bond, so that it has double bonds in polymer chains and is poor in weather resistance, chemical resistance and reactivity.
U.S. Pat. Nos. 4,316,973 and 4,758,631 and Japanese Patent Kokai Publication No. 105005/1988 disclose polymers having an unsaturated group at a chain end. The polymer of U.S. Pat. Nos. 4,316,973 and 4,758,631 is prepared by an Inifer method comprising cationically polymerizing isobutylene in the presence of 1,4-bis(.alpha.-chloroisopropyl)benzene as a polymerization initiating and chain transfer agent and BCl.sub.3 as a catalyst and further reacting a formed polymer having a chlorine atom at a chain end.
A polymer disclosed in Japanese Patent Kokai Publication No. 105005/1988 is prepared by synthesizing an isobutylene polymer having chlorine atoms at both chain ends by the Inifer method and, just after synthesis or purification, reacting the isobutylene polymer with allyltrimethylsilane to obtain a polymer having allyl groups at both chain ends.
However, the polymers disclosed in U.S. Pat. No. 4,316,973 and Japanese Patent Kokai Publication No. 105005/1988 require multiple steps for the production and/or expensive raw materials.